The present invention relates to the field of electrosurgery and, in particular, to electrosurgical devices and methods which employ high frequency voltage to cut, ablate or coagulate tissue.
Electrosurgical procedures typically rely on the application of very high frequency or radio frequency (RF) electrical power to cut, ablate or coagulate tissue structures. For example, electrosurgery cutting entails heating tissue cells so rapidly that they explode into steam leaving a cavity in the cell matrix. When the electrode is moved and fresh tissue is contacted, new cells explode and the incisions is made. Such electrosurgical cutting involves the sparking of the current to the tissue, also known as the jumping of the RF current across an air gap to the tissue.
Radiofrequency electrodes employed in electrosurgical procedures are generally divided into two categories: monopolar devices and bipolar devices. In monopolar electrosurgical devices, the RF current generally flows from an exposed active electrode through the patient""s body, to a passive or return current electrode that is externally attached to a suitable location on the patient""s skin. In bipolar electrosurgical devices used in general surgery, both the active and the return electrodes are exposed and are typically in close proximity. The RF current flows from the active electrode to the return electrode through the tissue. Thus, in contrast with the monopolar electrosurgical devices, the return current path for a bipolar device does not pass through the patient.
Electrosurgery which takes place in a conductive fluid environment, such as inside of a joint or body cavity filled with, for instance, normalized saline solution, differs from that described previously in that current is conducted from the active electrode through the fluid to the return electrode. In the case of a monopolar device, the current flows through the patient to the return electrode in the manner previously described. In the case of bipolar devices operating in a conductive fluid environment, the return electrode is not in contact with tissue, but rather is submerged in the conductive fluid in the proximity of the active electrode. Current flow is from the active electrode through the conductive liquid and surrounding tissues to the return electrode of the bipolar device. Whether an electrode is monopolar or bipolar, current flows from all uninsulated surfaces of the active electrode to the return electrode anytime that the electrode is energized. This is in contrast to conventional surgery (also called xe2x80x9copen surgeryxe2x80x9d) in which current flows only through electrode surfaces in contact with the patient""s tissue.
For an electrode in a fluid environment to vaporize tissue, as in the cutting process described previously, the current density at the electrode/tissue interface must be sufficiently high to cause arcing between the electrode and the patient. If such current density is not achieved, power flows from the active electrode to the return electrode with no desirable clinical effect. In fact, such current flow is highly undesirable since the current flowing from the active electrode heats the conductive fluid in the region surrounding the active electrode. A surgeon using a device which is energized but not arcing to the tissue may believe that he is not affecting tissue in close proximity to the active electrode, however, he may be subjecting the tissue to temperatures approaching 100xc2x0 C. Even when the electrode is arcing to the tissue, the thermal effects are not limited to vaporization of the tissue. Appreciable undesirable heating of the fluid and tissue in the vicinity to the electrode takes place.
One way of avoiding the negative effects of the undesirable heating of the fluid and adjacent tissue structures is to set the power of the electrosurgical generator to a level that is low enough to minimize the heating of the liquid, but high enough to produce sparks. There is an inherent difficulty, however, in achieving acceptable electrosurgical parameters, since virtually all electrosurgical electrodes are xe2x80x9cignited,xe2x80x9d i.e., generate sparks, only when brought into contact with tissue, and then, generally, after a time delay of varying lengths. In addition, during electrosurgical procedures, if no sparks are generated, most of the RF power supplied to an electrode operating in a conducting fluid is dissipated in the fluid itself as heat, consequently raising the temperature of the fluid within the joint and the adjacent tissue. If sparks are generated, large fraction of the RF power is used for the creation of sparks in the vicinity of the electrodes, and small fraction heats the surrounding liquid and patient body. Therefore, energizing the electrosurgical electrode without instant initiation of sparks is dangerous and undesirable, as the heating may damage tissue structure uncontrollably in surrounding areas.
Except at very high power levels, monopolar and bipolar electrosurgical electrodes ablators are incapable of generating sparks until they are in contact with tissue, and even then, not instantly. This often substantial delay in spark generation unnecessarily increases the time the probe must be in contact with tissue structure increasing the probability of damage to surrounding tissue structures. During the period when the electrosurgical electrode is energized but before sparking, the heating of the fluid is continuing without any beneficial effect to the patient. This undesirable heating substantially increases the chance of patient burns.
Accordingly, there is a need for an improved electrode for electrosurgical ablation of tissue structures in a conductive fluid which is capable of easy ignition, especially at low power levels. An efficient design for an electrosurgical electrode operating at a low RF power level, as well as methods of fabricating such electrosurgical electrode and methods of utilizing such an electrode in various electrosurgical procedures are also needed.
In one aspect, the invention provides an electrosurgical electrode capable of achieving instant ignition in a conductive fluid. According to one embodiment, the electrosurgical electrode for instant ignition in a conductive fluid comprises a metallic body portion of various geometries, a metallic tip and a dielectric insulator adjacent the metallic body portion. The metallic tip is recessed from the surface of the dielectric so that the dielectric material and the adjacent recessed metallic tip form a high current density zone for bubble entrapment and instant spark formation. According to another embodiment, lateral walls of the recessed metallic tip form an incidence angle with adjacent dielectric walls, so that the dielectric material and the adjacent recessed angled metallic tip form another high current density zone for bubble entrapment and spark formation. The high current density zones interrupt the conventional flow of fluid and lead to more bubbles sticking to these zones and, thus, to a more efficient creation of steam bubbles. Regardless of whether the metallic tip of the electrode is in contact with a target tissue, spark generation is instantaneous.
In another aspect, the invention provides an apparatus for conducting electrosurgical procedures or interventions comprising at least one electrosurgical probe that includes a shaft having a proximal end and a distal end. The distal end supports at least one electrosurgical electrode for instant ignition in a conductive fluid and comprising a metallic electrode recessed from the surface of the dielectric for about 0.1 to about 5 millimeters. The metallic electrode may have a metallic tip having its lateral walls at an incidence angle with adjacent dielectric walls of about 10 to 80 degrees, more preferably of about 35 to 55 degrees. Alternatively, the metallic tip may comprise a plurality of metallic protuberances of various geometrical forms.
The invention also provides a method of forming an electrosurgical electrode by recessing a metallic electrode from the surface of a dielectric insulator adjacent the metallic electrode for about 0.1 to about 5 millimeters, and forming at least one high current density zone for bubble trap and spark formation. The metallic electrode may be further constructed so that the metallic tip at the proximal part of the metallic electrode has lateral walls at an incidence angle with adjacent dielectric walls of about 10 to 80 degrees, more preferably of about 35 to 55 degrees. Alternatively, the metallic tip may be shaped into a plurality of metallic protuberances with various geometrical forms.
The invention also provides a method of employing an electrosurgical electrode in an electrosurgical procedure for which the total time the electrode needs to be in contact with the tissue structure is decreased. The method comprises the steps of: (i) positioning an electrosurgical electrode adjacent a target tissue, the electrosurgical electrode comprising a metallic electrode recessed from the surface of a dielectric, and then (ii) either submerging the target tissue in an electrical conducting fluid or (iii) directing an electrically conducting fluid to the target tissue to allow the formation of a high current density zone for bubble trap and spark formation in the region formed by the dielectric material and the adjacent recessed portion of the metallic electrode.
These and other features and advantages of the invention will be more apparent from the following detailed description that is provided in connection with the accompanying drawings and illustrated exemplary embodiments of the invention.